Introduce AttachmentStore metadata record

sync/internal_api/public/attachments/on_disk_attachment_store.h

Index: sync/internal_api/public/attachments/on_disk_attachment_store.h
diff --git a/sync/internal_api/public/attachments/on_disk_attachment_store.h b/sync/internal_api/public/attachments/on_disk_attachment_store.h
index d74b60bf60895fe66b56a1d1df9052fc83c685db..fdd9f33ab2d07c71632434ce228548941abfb90c 100644
--- a/sync/internal_api/public/attachments/on_disk_attachment_store.h
+++ b/sync/internal_api/public/attachments/on_disk_attachment_store.h
@@ -13,12 +13,17 @@
 #include "sync/api/attachments/attachment_store.h"
 #include "sync/base/sync_export.h"
 
+namespace attachment_store_pb {
+class AttachmentStoreMetadata;
+}  // namespace attachment_store_pb
+
 namespace base {
 class SequencedTaskRunner;
 }  // namespace base
 
 namespace leveldb {
 class DB;
+class Status;
 }  // namespace leveldb
 
 namespace syncer {
@@ -49,7 +54,13 @@ class SYNC_EXPORT OnDiskAttachmentStore : public AttachmentStoreBase,
   Result OpenOrCreate(const base::FilePath& path);
 
  private:
-  std::string CreateDataKeyFromAttachmentId(const AttachmentId& attachment_id);
+  static leveldb::Status ReadStoreMetadata(

[maniscalco, 2014/10/21 21:41:03]

Light suggestion: unless you need them to be part of the class, consider moving
these functions to an anon namespace in the .cc file.

[pavely, 2014/10/24 20:42:55]

Done.

+      leveldb::DB* db,
+      attachment_store_pb::AttachmentStoreMetadata* metadata);
+  static leveldb::Status UpdateStoreMetadata(
+      leveldb::DB* db,
+      const attachment_store_pb::AttachmentStoreMetadata& metadata);
+  std::string MakeDataKeyFromAttachmentId(const AttachmentId& attachment_id);
 
   scoped_refptr<base::SequencedTaskRunner> callback_task_runner_;
   scoped_ptr<leveldb::DB> db_;